Various different types of electro-optic display devices are known, including liquid crystal display devices, electrophoretic display devices, electrochromic display devices, etc. A recently developed type of electro-optic display device is an electrowetting display device, as described amongst others in international patent applications WO 2003/071346 and WO 2005/098797.
International patent application WO 2005/036517 describes an electrowetting display apparatus having an active matrix display device, in which reset pulses are applied to image regions in order to improve the quality of the display. The pulses in this disclosure are also called preset pulses, because they are applied prior to the voltage setting an image region in a display state. In the case of segmented electrodes, preset pulses may also be applied when driving the electrowetting elements of the display device.
It has been found to be desirable to apply reset pulses also during the time an image region has a certain display state. Without the application of reset pulses, the electrowetting elements which are switched to an open state may become less effective at maintaining their display state. Such reset pulses can be applied advantageously for both active matrix display devices, segmented electrowetting display devices which have a direct drive scheme and passive matrix display devices.
For explanatory purposes, a prior art display driving system which could be suitable for applying a reset pulse scheme is illustrated in FIGS. 9 to 12. Referring to FIG. 9, in the prior art arrangement, the display driving system receives data from a microcontroller. In some embodiments, the microcontroller might be physically incorporated within the total display driving hardware. An input data interface provides data to a display controller 4 which in turn drives an output latch 6. Each of the segments of the display device is driven by a driver stage 8.
FIG. 10 illustrates the circuitry in a driver stage according to the prior art. The voltage applied across the electrowetting element Vew is generated by switching between a high voltage level Vout and ground. This is done by selectively actuating switches S1 and S2, implemented as transistors. In order to apply reset pulses, which may be of a form similar to that shown in FIG. 11, a switching scheme similar to that shown in FIG. 12 is used. A problem with this prior art arrangement is that, if a reset pulse is applied frequently and with short duration, the input data rate is relatively high. When a microcontroller supplies the input data, it must run at a relatively high frequency to deliver the input data, which may require a high power consumption. The same applies to the output latch.
It would be desirable to provide arrangements whereby it is possible to reduce the number of switching actions of the controller circuitry when applying a reset pulse scheme for an electro-optic display device, in particular, but not exclusively, an electrowetting display device.